if you are a newER,you may not know how to Change logo of ,let me give you a little guild.
has a default logo :
it will show in tag page,achieve page and home page as default post image.
only if you did not set your own featured image.
you can click the “set featured image” button to set your own post image:
when after uploading a image ,at the bottom,there is a “set featured image” button too.
after you set your own featured image,it will replace default.like this:
and if you want repalce the default logo,upload you own logo.gif to theme/
it will work,and you better use same width and height image as default logo.gif which is 65PX × 65PX